Unsaturated polyester resins have been used in varied applications, such as in polyester vehicle body filler systems and glass reinforced polyester vehicle body filler systems used in the automotive body repair field. Galvanized (anti-corrosion) coatings inherently interfere with the interfacial cure and adhesion of all materials cured by free-radical polymerization, including polyester resin formulations. It has been known that polyester adhesion to metal can be improved by the use of adhesion promoters, the use of low molecular weight polymers with reduced monomer content, the use of metal pretreatments, or by accelerating the cross-linking reaction. Unfortunately, it has not been possible to achieve a highly flexible polymerized mastic that was both easily sandable and does not require the costly use of pre-treatments or adhesion promoters; the present invention overcomes this deficiency.
In the case of galvanized substrates, the poor adhesion problem is aggravated by the fact that the galvanize (zinc) retards curing of the resin system, delaying sanding and further operations on the filler, and, in some cases, may prevent a full cure. Additionally, as vehicle body constructs are increasingly made of lighter weight aluminum, high-strength steel, composite, and thermoplastic materials, vehicle body fillers need to be developed that can adhere to substrates with a broad range of surface energies.
Another dynamic in the automotive repair aftermarket industry is the increased regulatory concerns regarding the usage of styrene. Unsaturated polyester resin is a condensation product of dicarboxylic acids or anhydrides with di-, or poly-functional alcohols that traditionally have been dissolved in styrene as a reactive diluent. While unsaturated polyesters have been developed in the past as detailed for example in U.S. Pat. No. 6,268,464; these polyesters have been found unacceptable as vehicle body fillers owing to brittleness and excessive hardness.
Thus, there exists a need for a polyester resin that is capable of providing adhesion to metallic automotive body panels without resort to the use of pre-treatments or adhesion promoters. There still further exists a need for such a polyester resin formulation that is free of styrene.